1. Field of the Invention
The present invention relates to a thermoelectric system to supply power (electric energy) generated by a thermoelectric power generator which generates electricity by utilizing an outside temperature difference to a load so as to operate the load. The present invention especially relates to a thermoelectric system which provides a function to adequately control power supply from a thermoelectric power generator to a load, compensating for an influence of the Peltier effect peculiar to the thermoelectric power generator.
2. Description of the Related Art
There exists a thermoelectric system which generates electric power from heat energy caused by an outside temperature difference using a thermocouple and drives electronic equipment such as an electronic timepiece and the like utilizing electric energy obtained from the power generation.
An electronic timepiece driven by generated power from a thermoelectric power generator shown in FIG. 6 can be cited as a conventional example, which applies such a thermoelectric system to a small portable electronic device.
The electronic timepiece has a configuration in which a load means 20 is connected to the thermoelectric power generator 10 and power generated by the thermoelectric power generator 10 can be used with the load means 20.
The load means 20 is configured with a voltage-up converter 23, a timekeeping means 21 and an accumulator 22. The voltage-up converter 23 is connected to the thermoelectric power generator 10 and raises the voltage to twice that of the voltage generated by the thermoelectric power generator 10.
The timekeeping means 21 having a time-clock function and the accumulator 22 which is a second battery are connected in parallel to an output side of the voltage-up converter 23, and the accumulator 22 is charged by a voltage-up output of the voltage-up converter 23 to supply the charged power to the timekeeping means 21.
Furthermore, the electronic timepiece is provided with a generated voltage detector 35 using an amplifier circuit to detect the generated voltage of the thermoelectric power generator 10, and a controller 36 to control operation of the voltage-up converter 23 in accordance with the detected voltage.
The thermoelectric power generator 10 is configured to connect plural thermocouples in series. In the case that the electronic timepiece in this example is a wrist watch, the thermoelectric power generator 10 is disposed so that a warm junction side is contacted with a case back of the wrist watch and a cold junction side is contacted with the case which is insulated against heat from the case back. Heat energy created by a temperature difference between the case back which closely contacts an arm of the person who carries the wrist watch and the case exposed to the outside air, is converted to electric energy.
In an electronic time piece utilizing such a conventional thermoelectric system, generated voltage by the thermoelectric power generator 10 is raised by means of the voltage-up converter 23 after being charged to the accumulator 22 and then used to operate hand-driving of the timekeeping means 21 and the like with the charged electric energy.
At this time, when the generated voltage of the thermoelectric power generator 10 detected by the generated voltage detector 35 exceeds a predetermined value, the controller 36 considers that the generated power of the thermoelectric power generator 10 is applicable and outputs a signal to operate the voltage-up converter 23. Through this process, the voltage-up converter 23 starts voltage-up operation to raise the generated voltage of the thermoelectric power generator 10 to charge the accumulator 22. On the other hand, when the generated voltage of the thermoelectric power generator 10 detected by the generated voltage detector 35 is less than a predetermined value, the controller 36 stops the voltage-up operation of the voltage-up converter 23 to stop power supply to the load means 20 from the thermoelectric power generator 10. At the same time, the controller 36 prevents electric energy charged in the accumulator 22 from discharging to the thermoelectric power generator 10 side.
In the conventional thermoelectric system, when the thermoelectric power generator 10 used for a power generating device is given a higher range of temperatures on the warm junction side and a lower range of temperatures on the cold junction side, the thermoelectric power generator 10 generates electricity through the Seebeck effect and outputs generated voltage (incidentally, the generated voltage caused by Seebeck effect is called thermal electromotive force). Especially, when the thermoelectric power generator 10 has no load, generated voltage proportional to the temperature difference existing between its own warm and cold junctions can be obtained from the thermoelectric power generator 10.
However, when a load is connected to take out power from the thermoelectric power generator 10, current flows from the thermoelectric power generator 10 to the load. The current causes the Peltier effect which is a reaction of the Seebeck effect and a phenomenon which reduces the temperature difference given to the thermoelectric power generator 10. That is, when current flows from the thermoelectric power generator 10 to the load, an exothermic reaction occurs on the cold junction side and an endothermic reaction takes place on the warm junction side. Through this Peltier effect, the temperature difference existing in the thermoelectric power generator is reduced, such that the generated voltage which is a thermal electromotive force is also reduced.
However, in the conventional thermoelectric system, temporary reduction of the thermal electromotive force caused by the Peltier effect is not considered, and the temporary reduction of the thermal electromotive force is merely considered to be the result of a temperature change in the outside circumstances.
Therefore, if the thermoelectric system is configured to switch between operation and suspension of the voltage-up converter in accordance with the magnitude of the generated voltage of the thermal power generating device as above, there exists a disadvantage that the voltage-up converter repeatedly performs the operation and the suspension when the value of the generated voltage is close to the detection threshold value.
That is, when a thermoelectric system is configured to switch between supply and suspension of power to a connected load in accordance with the value of generated power from a thermoelectric power generator, it becomes impossible to precisely measure the thermal electromotive force while the load is in operation. As a result, there may be cases where generated power from the thermoelectric power generator can not be used effectively.